Vinyl esters of higher carboxylic acids are of some economic importance as comonomers. They can be used to modify the properties of polymers, for example polyvinyl chloride, polyvinyl acetate, polystyrene or polyacrylic esters. Thus, for example, the hydrolysis resistance of emulsion paints can be increased. Vinyl esters of higher carboxylic acids are also used for the production of adhesives. Vinyl esters based on 2-ethylhexanoic acid, isononanoic acid, lauric acid or the Versatic acids 911, 10 and 1519 from Shell are of industrial importance for these fields of use. These higher carboxylic acids can be obtained, for example, by oxidation of aldehydes which are prepared by the oxo process or by the Koch synthesis from the olefin, carbon monoxide and water. In the case of vinyl esters based on 2-ethylhexanoic acid, lauric acid or isononanoic acid, if the isononanoic acid consists predominantly of 3,5,5-trimethylhexanoic acid, uniform compounds are present, while in the case of vinyl esters of the Versatic acids 911, mixtures of highly branched carboxylic acids having from 9 to 11 carbon atoms, and in the case of vinyl esters of the Versatic acids 1519, mixtures of highly branched carboxylic acids having from 15 to 19 carbon atoms, are present in the vinyl ester. In the case of vinyl esters of Versatic acid 10, structurally different highly branched decanoic acids such as neodecanoic acids are derivatized.
Vinyl esters can be prepared by reaction of isononanoic acids with acetylene, preferably in the presence of zinc salts at temperatures of 200-230° C. (G. Hübner, Fette, Seifen, Anstrichmittel 68, 290 (1966); Ullmanns Encyklopädie der technischen Chemie, 4th edition, 1983, Verlag Chemie, volume 23, pages 606-607; EP 1 057 525 A2) or by the transvinylation reaction with a vinyl ester of another carboxylic acid, frequently vinyl acetate or vinyl propionate, in the presence of transition metal catalysts (Ullmanns Encyklopädie der technischen Chemie, 4th edition, 1983, Verlag Chemie, volume 23, pages 606-607; Adelmann, Journal Organic Chemistry, 1949, 14, pages 1057-1077; DE 199 08 320 A1, EP 0 497 340 A2, WO2011/139360 A1, WO2011/139361 A1).
The C4 fraction from the steam cracking of naphtha serves as raw material for the industrial preparation of isononanoic acid. Its availability compared to the C2 and C3 cracking products can be controlled by means of the conditions of the steam cracking and is guided by market circumstances. 1,3-butadiene is firstly removed from the C4 cracking product by extraction or by selective hydrogenation to form n-butenes. The C4 raffinate obtained, also referred to as raffinate I, contains predominantly the unsaturated butenes isobutene, 1-butene and 2-butene and also the hydrogenated products n-butane and isobutane. In the next step isobutene is removed from the raffinate I and the isobutene-free C4 mixture obtained is referred to as raffinate II.
In industrial production, the removal of isobutene is carried out using various processes in which the relatively high reactivity of isobutene in the raffinate I is exploited. The reversible proton-catalyzed molecular addition of water to form tert-butanol or the molecular addition of methanol to form methyl tert-butyl ether are known. Isobutene can be recovered again from these addition products by redissociation (Weissermel, Arpe, Industrielle Organische Chemie, VCH Verlagsgesellschaft, 3rd edition, 1988, pages 74-79).
Likewise, the butadiene-free C4 raffinate can be brought into contact with an acidic suspended ion exchanger at elevated temperature and under superatmospheric pressure. Isobutene oligomerizes to diisobutene, triisobutene and to a small extent to higher oligomers. The oligomers are separated off from the unreacted C4 compounds. Diisobutene or triisobutene can then be obtained in pure form from the oligomerization mixture by distillation. Codimer is formed to a small extent by dimerization of n-butenes with isobutene (Weissermel, Arpe, Industrielle Organische Chemie, VCH Verlagsgesellschaft, 3rd edition, 1988, page 77; Hydrocarbon Processing, April 1973, pages 171-173).
Diisobutene, either prepared by oligomerization of pure isobutene obtained by redissociation or obtained during the course of the work-up of a butadiene-free raffinate I, is subsequently converted into a C9 derivative which has one more carbon atom. Hydroformylation or the oxo process, in which diisobutene is converted by means of carbon monoxide and hydrogen in the presence of rhodium or cobalt catalysts into the corresponding aldehyde, is operated industrially. Since diisobutene contains predominantly the octenes 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene, the hydroformylation reaction gives the C9-aldehyde 3,5,5-trimethylhexanal as main constituent. Further C9 isomers which are present in small amounts are 3,4,4- and 3,4,5-trimethylhexanal and also 2,5,5-trimethylhexanal, 4,5,5-trimethylhexanal and 6,6-dimethylheptanal. Oxidation of this aldehyde mixture gives an industrially available isononanoic acid which usually has a content of 3,5,5-trimethylhexanoic acid of about 90% (Ullmanns Encyklopädie der technischen Chemie, 4th edition, 1975, Verlag Chemie, volume 9, pages 143-145; EP 1 854 778 A1).
Diisobutene can likewise be converted by means of hydrocarboxylation or the Koch reaction with carbon monoxide and water in the presence of sulphuric acid into the highly branched isononanoic acid 2,2,4,4-tetramethyl-1-pentanoic acid. Owing to the double alkyl branching on the carbon atom adjacent to the carboxyl group, this isononanoic acid is frequently also referred to as neononanoic acid. (Ullmanns Encyklopädie der technischen Chemie, 4th edition, 1975, Verlag Chemie, volume 9, pages 143-145).
The n-butenes present in the raffinate II after removal of isobutene are also converted industrially into butene oligomer mixtures from which the isomeric octenes are separated off and converted by hydrocarboxylation into the corresponding isononanoic acids (DE 199 08 320 A1; EP 1 029 839 A1). The oligomerization of n-butenes is carried out industrially over acidic catalysts such as zeolites or phosphoric acid on supports. This gives octenes which contain dimethylhexenes as main product. Further processes which may be mentioned are the DIMERSOL process and the OCTOL process. The DIMERSOL process is carried out using soluble nickel complex catalysts and leads to an octene mixture having a high proportion of 3- and 5-methylheptenes together with dimethylhexenes and n-octenes. In the OCTOL process, supported fixed-bed nickel catalysts are used and the octene mixture obtained has a low degree of branching (DE 199 08 320 A1, WO 03/029180, Hydrocarbon Processing, February 1986, pages 31-33). According to DE 199 08 320 A1, the respective, differently branched octene mixtures are converted by means of hydrocarboxylation into the corresponding isononanoic acids which are subsequently converted into the corresponding vinyl esters. Vinyl esters of isononanoic acids which are based on an octene mixture from the OCTOL process are suitable as plasticizing comonomer.
In view of the fact that the availability of octenes based on the C4 fraction from naphtha cracking is limited and depends on local site conditions, it is desirable to open up further octene sources on the basis of inexpensively available bulk products which can be transported in a simple way to the various sites. 2-Ethylhexanol is available at low cost as an industrial bulk product and can be marketed widely without problems. 2-Ethylhexanol is, as is known, prepared industrially by hydroformylation or oxo reaction of propylene to form n-butyraldehyde with subsequent alkali-catalyzed aldol condensation to form 2-ethylhexenal and subsequent total hydrogenation to 2-ethylhexanol (Ullmanns Encyklopädie der technischen Chemie, 4th edition, 1974, Verlag Chemie, volume 7, pages 214-215).
The use of 2-ethylhexanol for preparing an octene mixture which is processed by dehydration, hydroformylation and hydrogenation to give an isononanoic mixture, is briefly described in WO 03/029180 A1. Here, setting of the viscosity of the isomeric alkyl phthalates which are obtained by esterification of isomeric nonanols with phthalic acid or phthalic anhydride is the main focus. Information as to how to convert the dehydration products of 2-ethylhexanol into isononanoic acid is not given.
The utilization of 2-ethylhexanol as octene source makes it possible to provide the vinyl ester of isononanoic acid on the basis of propylene and reduces the dependence on the availability of octenes based on butene.